Smilediver's suggestion seconded. For storing block data like that, text files are always dead simple. You can easily edit them by hand with a text editor and they are trivial to read/write. Using a bitmap file (like a png or bmp file) might be a little easier to edit graphically, but aren't quite as easy to work with in code.

The other options you listed:
PList - Basically is a subset of XML with APIs that make it easy to read. Works well for structured data, but not so well for tilemaps.
XML - Libraries help, but XML is a pain to deal with.
Core Data, SQLite - Stay away from these unless you are storing massive amounts of data that changes often. They generally take quite a bit of code to set up, read or write data, and generally need lots of error handling code.